Variable speed tensile tester



June 9, 1964 P. c. WHARFF, JR.. ETAL 3,136,158

VARIABLE SPEED TENSILE TESTER 5 Sheets-Sheet 1 Filed Aug. 10, 1960 June9, 1964 P. c. WHARFF, JR., ETAL 3,136,158

VARIABLE SPEED TENSILE TESTER Filed Aug. 10, 1960 5 Sheets-Sheet 2 N \h\N a m xXk u qqgQU I Us 5 ATTORNEY June 9, 1964 P. c. WHARFF, JR., ETAL3,136,158

VARIABLE SPEED TENSILE TESTER 5 Sheets-Sheet 3 Filed Aug. 10. 1960INVENTOR5 MM%W/ ATTORNEY June 9, 1964 P. c. WHARFF, JR., ETAL 3,

VARIABLE SPEED TENSILE TESTER Filed Aug. 10, 1960 5 Sheets-Sheet 4ATTORNEY June 9, 1964 P. c. WHARFF, JR., ETAL VARIABLE SPEED TENSILETESTER 5 Sheets-Sheet 5 Filed Aug. 10. 1960 llllllllll 8 1 INVENTOR5MMCE C.

. ATTORNEY United States Patent 3,136,158 VARIABLE SPEED TENSILE TESTERPrentice C. Wharff, Jr., 3212 Los Palos Circle, Lafayette, Calif., andKenneth R. Oliver, Jr., 26 Woodhaven Road, Newport News, Va.

Filed Aug. 10, 1960, Ser. No. 48,716 16 Claims. (Cl. 7389) Thisinvention relates to tensile testers and is particularly directed to animproved apparatus for more accurately determining tensile properties ofspecimens, such as single fibers, filaments, and similar unitaryelements, and to provide for manual and automatic control of the equipment with a direct indication of the stress-strain characteristics ofsamples undergoing tests.

The measurement of stress-strain characteristics under various controlenvironmental conditions and at various rates of extension provideimportant information in fiber research work. It is important for theperformance of some tests that at least that portion of the apparatuswhich stresses the fibers be of small size and be remotely controllable,so that it may be operated in an environmental cabinet for certain typesof tests. It is also desirable that manual as well as automatic controlbe available for repetitively stressing and relieving specimensundergoing tests. In addition, it is desirable that the apparatus bebuilt in three cooperating and connected but physically separatedportions or units, which can be spaced from each other to provide moreversatility in the conduct and control of tests. These units prefer-ablycomprise a filament puller or stresser, a remote control box, and arecorder incorporating certain control circuits.

The filament puller or stresser basically incorporates the force andelongation transducers and drive systems. This portion of the apparatusis the part which preferably is made relatively small, so .that it canbe readily placed in an environmental cabinet, if desired. The drivemechanism for the filament puller may contribute very appreciably to itsadaptability for the performance of a variety of tests and comprisesgearing which can be readily replaced for different ratios of gearreduction to obtain a variety of rates of extension. In addition, amotor mounting is provided which facilitates replacement of the filamentpuller drive motor, so that motors for direct drive or gear motors maybe easily interchangeably mounted for driving the filament pullergearing at variouspredetermined rates. It also incorporates features 'inthe electri cal and mechanical drive system for stressing test sampleswhich provide a maximum degree of flexibility with respect to testsample lengths and modes of operation. Among these is an arrangement forthe rapid return of the extension yoke, which is independent of theextension drive rate and independent of the normal motor return drive.In addition, this part of the apparatus incorporates a reversible drivewhich provides for the performance of hysteresis tests, as well asstress-strain tests for determining the modulus of elasticity, elasticlimit, yield point, and maximum or ultimate strength characteristics oftest samples.

The remote control box preferably includes the various circuit making,breaking, andchanging devices for man ually and automaticallycontrolling the operation of the filament puller, which devices are notprimarily governed by characteristics of the sample undergoing tests.This facilitates the performance of the various tests under controlledambient conditions and provides for emergency control of the operationof the filament puller. In addition, the remote control box is providedwith position or condition indicating signal devices which inform anoperator of the position or condition of certain parts of the filamentpuller mechanism. It preferably also is provided with a suitablecontrol, such as apotentiometer, for varying the response of therecorder with the cross section of -a test sample, so as to indicatestress per unit cross sectional area. These all cooperate to adapt theapparatus to the performance of a wide variety of tensile tests.

The recorder portion of the apparatus may comprise any suitabletwo-coordinate recorder capable of plotting a curve along thecoordinates representative of the stress strain characteristics of thetest specimen. This recorder preferably is provided with certainautomatic circuit controlling members, which are primarily responsive tocharacteristics of the test specimen as determined by the filamentpuller and transmitted to the recorder as suitable electrical signals.Some of these circuit controlling members may be rendered non-responsivefor the performance of certain types of tests, and, in a simplified formof the present apparatus, certain of these circuit controlling membersmay be entirely omitted. These characteristicresponsive circuitcontrolling members in the recorder may take the form of a series ofmicroswitches operable in response to the desired control conditions forclosing or opening circuits which govern the operation of certainaspects of the filament puller mechanism.

Among such control members may be one arranged to assure a trueindication of strain or elongation of a test sample. This member mayconveniently comprise a suitable microswitch operable by the recorderafter the test sample has been placed under a predetermined stress, suchas 2 percent of the maximum stress which can be indicated or recorded bythe recorder. This assures against a false indication of strain orelongation of a test sample while the filament puller is merely beingdriven to the point Where stress is about to be applied to the specimen,as might readily occur if the initial specimen were curled or kinkedsuch that it would be necessary to straighten the test filament prior tothe actual application of stress thereto.

Another control member in the recorder may comprise a microswitch whichis responsive to stress reversal as indicated by the operation of therecorder, as when a filament breaks. This member preferably controls acircuit for stopping the operation of the filament puller drivemechanism and for automatically operating the extension yoke rapidreturn mechanism. Under certain conditions, as for the performance ofhysteresis tests, this latter stress reversal responsive control must berendered inoperative, so that the test sample may be repetitivelystressed and relieved of stress, under controlled rates of operation ofthe filament puller in opposite directions. .For such tests, theextension yoke rapid return device must remain in inoperative condition.Furthermore, for determining hysteresis characteristics of a testsample, it might be desirable automatically to decrease the stress on asample beyond a predetermined strain and automatically to restress thesample when the strain has been reduced to zero. It also may bedesirable to vary the predetermined strain at which the decrease instress automatically begins, so that a variety of hysteresischaracteristics may be obtained. These features may be obtained byproviding suitable microswitches on the recorder whichcontrol thedirection of rotation of the extension yoke drive motor and provide forthe response of these microswitches to predetermined strain values asindicated by the recorder.

It also is desirable to provide for-rendering the filament pullerinoperative beyond a predetermined strain equivalent to the full scaledeflection of the recorder. This will prevent damage to the recorder andincludes an arrange ment for controlling the filament puller so as toreturn it to its initial or zero stress-strain position for thecommencement of another test.

An object of this invention is to provide an improved tensile tester.

Another object of this invention is to provide a tensile testerspecifically improved to perform tensile tests on single filamentspecimens, either under automatic or manual control.

A further object of this invention is to provide an improved tensiletester with features which are automatically operable in response to theoccurrence of certain predetermined conditions.

Still another object of the'present invention is to provide a versatiletensile tester which will give a direct indication of the stress-strainrelationship of a specimen undergoing a tensile test, with a correctionof the relationship to indicate the force per unit cross sectional areaof the test specimen.

A yet further object of the present invention is to provide a tensiletester which is particularly constructed for testing single filamentspecimens in controlled ambients.

Yet another object of this invention is to provide an improved tensiletester for performing hysteresis tests on relatively small filaments,either automatically or under manual control.

An additional object of this invention is to provide an improvedfilament tensile tester with safety features for rendering the testmechanism inoperative and returning it to its zero or initial startingposition under certain conditions which might result in damage to theequipment.

Further objects and advantages of this invention will become apparentfrom the following description, referring to the accompanying drawings,and the features of novelty which characterize this invention will bepointed out with particularity in the claims appended to and forming apart of this specification.

In the drawings:

FIG. 1 is a perspective view of a tensile tester made in accordance withthe present invention, partsof which are schematically illustrative ofcertain members of the apparatus, particularly of those within therecorder;

FIG. 2 schematically illustrates the tensile tester shown in FIG. 1,giving details of the electrical circuits of the apparatus;

FIG. 3 is a side elevational view of the tensile tester filament pullershown in FIG. 1, partially broken away and partially schematicallyillustrated, showing the operative relationship of parts of the drivingmechanism of the filament puller taken along a broken section indicatedby line 3-3 in FIG. 4;

FIG. 4 is a side elevational view taken along line 4-4 of FIG. 3, partlybroken away and partly in section, illustrating further the detailedrelationship of certain parts of the driving mechanism for the extensionyoke of the filament puller;

' FIG. 5 is a sectional view of the lower bearing guide block for theextension yoke of the filament puller, taken along line 5-5 of FIG. 3;

FIG. 6 is a sectional side elevational view of the filament puller,taken along line 66 of FIG. 3, showing the arrangement of the externalgear train for driving the elongation measuring potentiometer; and

FIG. 7 is a fragmentary plan view showing the mounting of the drivemotor in the housing.

Tensile testers are useful in determining tensile characteristics ofvarious types of materials which may be used for many purposes, varyingfrom a rubber band or a fiber used in the production of fabric orclothing to metallic elements which may be used for many purposes frommusical instruments to large structural beams and tie members. All suchstructural elements have certain fundamental characteristics which havebecome recognized in the trades as indicative of certain qualities ofthe elements and of the materials of which they are composed. The mostimportant of the tensile properties are generally those which may beillustrated by a stress-strain curve and which may be determined by suitable tensile tests.

Until relatively recently the testing of single fiber or filamentspecimens was undertaken primarily as a matter of academic interest.This was due primarily to the fact that until recent years fibers usedin the manufacture of fabrics generally were natural products obtainablefrom natural sources, such as wool, cotton, flax, etc., over theproduction of which little control could be exercised. With the adventof synthetic fibers, it has become important to the fiber manufacture tobe able to determine and predict tensile properties, both for theimprovement of the synthetic fibers and to enable the manufacturer to beable to specify the physical properties of fibers to assure the qualityof materials which he sells or uses for the manufacture of textileproducts.

The properties of single fibers or filaments have, therefore, become thecommon ground between the fiber and textile manufacturers, andconsequently reliable tests for determining the tensile properties ofsingle fibers have become very important. Furthermore, the behavior offibers in different ambients is of considerable importance, as testsunder one set of ambient conditions may very well provide results whichare very materially different from those obtainable in a .dilferentenvironment. It, therefore, becomes important to be able to test thephysical properties of single fibers or filaments under a'variety ofambient conditions and directly to compare the results of such tests.

The illustration of test results by stress-strain curves not onlyfacilitates a comparison of tensile properties of a particular type offiber under different ambient conditions, but also facilitates thecomparison of tests of different types of fibers under the same ambientconditions. Such stress-strain curves readily yield importantinformation by a simple inspection of the curves. Among the importantphysical characteristics indicated by such curves is the well-knownYoungs modulus, also known as the modulus of elasticity or elasticmodulus, which is represented in a stress-strain curve by asubstantially straight line portion wherein a unit stress per unit crosssectional area produces a definite deformation per unit length of thespecimen. This elastic modulus also may be used to represent the stressbelow a certain value which will produce a definite deformation of aspecimen, from which deformation the specimen will return to itsoriginal dimensions when the stress is removed without any resultingpermanent deformation of the specimen.

This elastic characteristic of materials occurs at stresses below avalue known as the elastic limit of the material which generally appearsas a definite knee or bend in the stress-strain curve, just slightlybelow the yield point or yield strength. Stress beyond the elastic limitcauses permanent deformation of the specimen, although it may not besufiicient to cause breaking of it. As a rule, it is desirable tocontinue a tensile test until the specimen actually breaks, so that itsmaximum strength under stress can be determined. This maximum strengthis known as the tensile or ultimate strength of the specimen beingtested and is indicated by a final sharp break in the stressstraincurve. In some instances, the curve between the terminal points markedby the yield point and the ultimate strength point may be ofconsiderable importance as the specimen may continue to elongate withsubstantially no additional load at a point slightly beyond the elasticlimit of the specimen. This may prove to be very undesirable for certainuses as it might result in an excessive permanent elongation of materialformed of the fibers which will make the material useless for itsoriginally intended purpose.

In addition, it is desirable to be able to determine hysteresischaracteristics of fibers, as for many purposes materials formed offibers are subjected to repeated tension and it is highly desirable thatthe materials be restored to their original condition with substantiallyno permanent deformation. Certain fibers will be found to have differenthysteresis characteristics under different ambient conditions, and it,therefore, is very important to be able to determine whether or notfibers will have relatively uniform and permanent hysteresischaracteristics under different ambient conditions, or, if thecharacteristics vary, it is important to be able to predict the natureof such variations.

The design of any tensile tester must, therefore, be predicated upon aknowledge of the general range of quantities which the characteristicsof materials to be tested may possess. The embodiment of the presentinvention which is illustrated in the drawings represents a tensiletester which is especially useful for determining tensilecharacteristics of fine fibers and filaments. The general structuralarrangements and the control and indicating circuits can equally well beutilized for testing specimens of greater size and generally possessingcharacteristics wherein the stress and elongation may be many timesthose of small fibers and filaments. The present description andreference to the drawings generally will be limited to terminologyapplicable to the tensile tester shown, and such description is to betaken only as illustrative of an application of the present invention.

The illustrated embodiment of the present invention preferably is builtin three cooperating and connected but physically separated portions orunits, which can be spaced from one another to facilitate the control ofvarious tests. In addition, the mechanical drive of the tensile testeris adapted to provide different predetermined rates of operation. Theserates of operation should be definitely reproducible under widelyvarying conditions and at widely spaced intervals. This is obtained inthe illustrated embodiment by providing a separate filament puller 1,wherein drive motors each having a fixed speed may be quickly and easilyinterchanged for providing different rates of operation of the tensiletester. In addition, the illustrated tensile tester is constructed sothat readily interchangeable sets of gears can be mounted fortransmitting the driving power from the motor to the fiber-stressingmember at different gear ratios, so that for a given fixedspeed motor avariety of fixed rates of operation of the tensile tester also areobtainable.

The major control members and circuits of the tensile tester preferablyare incorporated in a single casing or control box 2, as shown in FIGS.1 and 2, which is separate from the filament puller and recorder. Thisprovides for the remote control of the operation of the tensile testerand can be used with a simple two-coordinate recorder or with a recorderhaving one or more of the auto matic control features shown in FIGS. 1and 2 which enable the performance of additional tensile testsresponsive to various conditions which are indicated by the recorder.Both the remote control box 2 and the recorder 3 are adapted to beconnected together and to the filament puller 1 by suitable plug typeterminals to facilitate arrangement of the different parts of theapparatus for different tests and to provide for interchangeably usingdifferent types of recorders.

In order to test fine fibers and filaments and to provide for a readycomparison of test results, it is desirable that the dimensions, such asthe cross sectional area and the length of the specimens, besubstantially constant for all comparable tests, so that the mechanicaland electrical systems can be designed to provide indications ofelongation or strain of the fibers in terms of a unit area and a unit ora constant gage length.

For any given material having a definite density the measurement of thesize of the fiber in terms of deniers provides a definite measurement ofthe cross sectional area of the specimen fiber, although the denier offibers technically is a measurement of the weight of the fiber for anypredetermined length. Artisans in the field of fibers, filaments,fabrics, and similar materials, generally refer to the denier of amaterial in order to indicate the size thereof, and, in view of thisgenerally accepted terminology, the term denier is used interchangeablywith the term cross sectional area in the present disclosure todesignate the size of specimen fibers and filaments.

With modern techniques for securely holding the ends of test specimens,it has been found that accurately comparable test results are obtainableby fixing the gage length of specimens and measuring or recordingelongation or strain of a specimen undergoing test after the specimenhas been subjected to a predetermined stress. This makes is possible torecord elongation or strain of a test sample directly by a recorderwithout the need of correcting for variations in gage length or reducingthe strain to terms of elongation per unit length or to a percentage ofgage length.

In the illustrated apparatus, a test, specimen fiber 4 is shown with theends thereof adhesively secured to tabs 5 and 6, so that the lengthbetween the ends of the specimen secured to the tabs is readilymaintained at a definite value. Details for thus securing filaments aredescribed in copending application Serial No. 851,336, K. R. Oliver,Jr., entiled Test Specimen Filament Mounting, filed November 6, 1959,now Patent 3,063,294, November 13, 1962. This type of mounting for testspecimens provides for quickly and easily mounting the specimen on thefilament puller portion of the present tensile tester, but othersuitable arrangements for holding the ends of test speci mens withoutdeformation may be used.

Each of the tabs 5 and 6 preferably is formed with an aperture 7therethrough, which can readily be slipped over an end 8 of a fasteninghook 9 secured in any suitable manner, as by a pair of nuts 10, to atension bar 11 of a suitable strain gage 12. The other end of thespecimen 4 secured to the tab 6 is adapted to be engaged by a tabgripping and holding element 13 securely fastened in any suitable mannerto an extension yoke base 14 against a shoulder 15 thereon. The holdingelement 13 preferably is formed with a pair of tab gripping claws 16which are separated by a narrow slot 17, substantially along thelongitudinal center line of the tab holding element 13. The tab 6 ismerely slid under the downwardly extending claws 16 with the end of thetest specimen 4 extending through the slot 17 out of engagement with theclaws 16 to provide a uniform and quick means for holding the lower endof a specimen. The base 14 is mounted on a drawbar 18 and is securedthereto in any suitable manner, as by a pin or set screw 19. The entiremember for holding the lower tab 6 is adapted to be operated by thefilament puller by being readily removably secured to an extension yoke20 by any suitable attaching means, such as conventional wedge blockclamping jaws 21. With such an arrangement, a specimen fiber 4 can bequickly and easily mounted between the strain gage hook 9 and theextension yoke claws 16, while the extension yoke 20 is in a raisedposition with the distance between the end 8 of the hook 9 and theunderside of the jaws 16 less than the distance between the securingportions of the tabs 5 and 6. Thus, when it is desired to stress thetest specimen 4, the extension yoke 20 is operated to take up the slackin the test specimen by being moved downwardly and eventually to exertforce on the lower end of the test specimen, which force is transmittedthrough the specimen to the tension bar 11 of the strain gage, whichmeasures this force as the stress on the specimen.

Preferably the strain gage 12 is of the unbonded resistor type, whichtransmits an electrical signal of an intensity which varies inaccordance with the magnitude of the tensile force transmitted to it bythe tension bar 11. The internal circuitry of such a gage is essentiallya Wheatstone bridge circuit connected between terminals 22, 23, 24, and25. This strain gage may comprise any conventional gage of this type,which can be suitably mounted on the filament puller. Such strain gagesoperate in accordance with the well-known principle that the resistanceof a conductor changes with its elongation,

so that a tension placed on certain terminals of the strain gage willunbalance the Wheatstone bridge.

In the illustrated system, energization of the strain gage bridgeisprovided by a suitable electrical source, such as a battery 26,connected across the gage terminals 22 and 24 through a suitablepotentiometer R The potentiometer R preferably is mounted in the remotecontrol box 2, while the battery 26 may be mounted in any convenientlocation, such as in the filament puller 1 or the remote control box 2.

The circuitry of the strain gage is conventional for gages of the typementioned and includes resistors R and R which are variably connectedtogether, preferably as shown in FIG. v2, across three of the straingage terminals to provide an adjustment of the electrical signalsobtainable across terminals 23 and 25 of the strain gage. These gageterminals are adapted to be connected through suitable conductors 27 toa Y-axis control 2-8 in the recorder 3, FIG. 1, which provides forplotting, on suitable coordinate paper in the recorder, thestressapplied to the test specimen 4. With this type of strain gagecircuitry, a potential difference is produced across the strain gageterminals 23 and 25 which is proportional to the tension on the straingage transmitted through the tension bar 11 from the test specimen 4.This is the potential difference which provides the electrical signaltransmitted by the conductors 27 to the recorder Y-axis drive control28.

This strain gage and its associated circuit provides a means for readilytransmitting the indication of stress on a specimen fiber to therecording instrument, such as the recorder 3 and acts as a very simplebasic force transducer which can easily be adjusted. to compensate forvariations in the cross sectional area of a test specimen. Generally,tensile test equipment indicates or records stress in terms of theactual force applied rather than in terms of force per unit crosssectional area. This is practical where the test specimen has arelatively large cross sectional area which can be held withinreasonably close limits. Synthetic fibers, as conventionally produced,often have relatively wide variations in cross sectional area, even whenproduced by the same equipment. This variation may be as much as percenteither way from the average for individual filaments. In view of thewide variation between production samples of single fibers,stress-strain curves in which the force or stress is plotted in terms ofgrams vs. elonga tion would have a 10 percent scatter on either side orthe average due simply to variations in cross sectional area. This wouldmake it extremely difficult to detect variations due to other factors.It is very important, therefore, that differences in cross sectionalarea be eliminated from the effects produced by the strain gagemeasurement of stress on a test specimen. This will result innormalizing of the stress-strain curves and provide an accurateexpression of the stress on a test specimen in terms of force per unitcross sectional area, such as grams per denier. This is the correctivefeature which is incorporated in the circuitry of the present'invention,including'the potentiometer R illustrated in FIGS. 1 and 2.

Preferably the potentiometer R is calibrated directly in deniers, whichmay be indicated on its control dial 29 mounted for easy visualobservation on the remote control box 2, FIG. 1. In this manner, thedenier of a test specimen can be determined beforehand, by a .vibro:

scope or otherwise, and, the control dial 29 of the denier potentiometerR may be set to indicate directly the denier of the test specimen,thereby providing a means for directly varying the response of thetension measure ment to stress on a test specimen in accordance with thecross section of the specimen. The shunting resistor R and the variablepotentiometer connection of the resistor R to the resistor R provides avoltage divider circuit between the strain gage terminals 22, 23, and24, by

which the electrical zero of the strain gage may be ad justed tocalibrate the gage to provide a proper response thereof to stress placedthereon.

In order to provide tensile tests which will yield practical informationregarding stress-strain characteristics of test specimens, it isdesirable that the tensile force applied to a specimen be applicable ina uniformly repeti tive manner, both to a single; specimen forhysteresis characteristics and for corresponding tests of differentspecimens. This requires that specimens undergoing tests be held in auniform manner and that the force be substantially uniformly andgradually varied. The tabs 5 and 6, to which the ends of the fiberspecimen 4 are secured, together with the strain gage hook 9 and the tabholding element 13 provide a means for uniformly holdin" the two ends ofa specimen for hysteresis test purposes and for tests of differentspecimens having predetermined gage lengths. Uniform application andvariation of tension on a test specimen may conveniently be provided bya drive mechanism for the extension yoke 2i) which moves the twospecimen holding members relative to each other at a predeterminablerate during the stressing of a specimen. Details of the extension yokedriving mechanism for thus stressing a specimen are illustrated in FIGS.3 and'4.

As shownin these figures, a filament puller drive motor M is providedwith a mounting flange 30, which can be easily slid into mounting slots31 formed in a supporting frame structure 32 supported in the housing 33of the filament puller 1. In order to assure a predeterminable fixedspeed of operation of the extension yoke 20, the drive motor Mpreferably is a synchronous motor, and, in most instances, comprises agear train mounted within the motor housing and driven by the motor, sothat the drive shaft 34 of the motor M will operate at a predeterminedrelatively low speed. Power for the motor M is supplied through suitableconductors 35 connected in the control system by an easily connectableplug type terminal member 36. Thus, if it is desired to operate thefilament puller at a diiferent predetermined speed, it is only necessaryto unplug the motor terminal 36, remove the motor M from the filamentpuller housing 33 by lifting it upwardly through the uncovered portion37, and replaceit with another drive motor M having the required speedof its output shaft 34 to provide the desired operating speed of theextension yoke 20. I

A suitable gear train is provided for connecting the motor drive shaft34 to the extension yoke 20, and includes a pinion gear 38 drivinglymounted on the motor output shaft 34. This gear 38 is adapted to have adriving engagement with a spur gear 39 secured in any suitable manner,as by a set screw 40, to a countershaft 41.

In order to assure proper driving engagement between the motor piniondrive gear 38 and the countershaft gear 39, an adjusting screw 42threadedly engages a boss 43, secured to the filament puller housing 33,and supports the motor flange 36 in the slot 31. As can more readily beseen by reference toFIG. 3, the adjusting screw 42 may be moved upwardlyor downwardly relative to the boss 43 and thereby adjust the position ofthe motor mounting flange 3i) upwardly and downwardly respectively inthe slot 31 with a corresponding adjustment of the pinion gear 38relative to'the countershaft gear 39. This assures a proper alignmentand proper driving engagement between the gears 38 and 39.

Power is transmitted from the countershaft 41 through a worm gear 44which is drivin'gly secured to the countershaft 41 in any suitablemanner, as by a locking key 45. The worm gear 44 has a drivingengagement with the teeth of a worm wheel 46 drivingly mounted on asecond countershaft 47 by any suitable means as by a set screw 48. Thiscountershaft 47 is rotatably mounted in suitable bearings 49 in amounting bracket hub 5'9, which is rigidly secured in any suitablemanner, as by screws 51, to the filament puller housing 33. This samemounting bracket is provided with a pair of arms 52 which extendupwardly and inwardly from the hub 50 and are formed with suitablebearing openings therein for rotatably supporting the countershaft 41,as is more clearly shown in FIG. 3. A readily interchangeable part ofthe extension yoke driving gear train is mounted on the exterior of thefilament puller housing 33 in order to provide for conveniently changingthis part of the gear train for obtaining various rates of operation ofthe extension yoke 20 with any given fixed-speed drive motor.

Such gear trains can be very easily computed to give different extensionrates with fixed centers for the shafts on which the different gears ofthe gear trains are mounted. These gears preferably all are in the formof spur gears and the mechanics of computing the number of gear teethand matching diameters need not be considered, as these involve onlyconventional computations which readily can be made to give the desiredresults.

This exteriorly mounted gear train includes a spur gear53 drivinglymounted on the countershaft 47 and arranged in driving engagement with adriven gear 54. This gear 54 is rotatably mounted on a stub shaft 55supported on the housing 33, and is of such size as to provide apredetermined speed reduction between the gear 53 and the gear 54. Thegear 54 preferably is formed with a hub 56 integral therewith and with asmaller spur gear 57. Spur gear 57 drivingly engages another spur gear58 which is drivingly mounted on driven shaft 59. This provides thefinal desired speed relation between the motor output shaft 34 and theinput to a main clutch CL The shaft 59 preferably is rotatably supportedby a suitable bearing in an end shield 68 of the clutch CL andinteriorly thereof, with suitable connections for transmitting powerfrom the driving motor M to the driven parts of the operating mechanismof the filament puller through this clutch. Preferably the clutch CL isof the electro-mechanical type, which provides for a positive drive andyet allows for substantially instantaneous de coupling under certaindriving conditions similar to overrunning or free-wheeling if thenormally driven member of the clutch operates at a higher speed than themember which normally is the driving member thereof.

The electrical part of the clutch allows this free-wheeling to takeplace while the mechanical part of the clutch provides for the positivedrive in either direction when power is being transmitted through theclutch from the motor M Any suitable conventional electro-mechanicalclutch, such as an electromagnetic clutch with a crown tooth mechanicaldrive, can be used to provide this main drive clutch connection of thedriving system. The electromag netic parts of the clutch may include asuitable energizing winding, preferably mounted in the drive member 61of the clutch, and the driven part of the electromagnetic portion of theclutch is mechanically connected to the crown tooth driving member ofthe mechanical portion of the clutch. The driven member 62 of the crowntooth portion of the clutch is mechanically connected to a main driveshaft 63 of the filament puller, and is rotatably mounted in bearingswithin the main clutch GL and in a suitable bearing 64 mounted in thefilament puller housing 33.

When power is transmitted from the drive motor M to the extension yoke20 through the main clutch CL and the main drive shaft 63, this power istransmitted through a spur gear 65 drivingly mounted on the shaft 63 andarranged in driving engagement With a gear rack 66, which may be formedintegrally with the extension yoke 20 or may be a separate member whichis fixedly and drivingly mounted on the extension yoke 20. The yoke islongitudinally slidably mounted in a bearing 67 supported in a collar 68secured to a cover 69 of the filament puller housing 33, and the otherend of the yoke 20 is longitudinally slidably supported in a specialguide bearing 70, FIG. 3. This guide bearing 70 has a partiallycylindrical opening 71 therein to receive the cylindrical portion of theextension yoke 20 and a substantially rectangular slot 72 broached orotherwise suitably formed in one side of the bearing in communicationwith the cylindrical opening 71. The cylindrical opening 71 of thebearing 70 supports and guides the extension yoke, and the rectangularslot 72 provides for the free passage therethrough of the gear rack 66as it is driven by the spur gear 65.

The upper end of the extension yoke 20 is provided with a quick-returnmechanism and includes a small threaded shoulder 73 of slightly lessdiameter than the major portion of the extension yoke on which the gearrack 66 is mounted, and a piston 74 mounted on this shoulder and securedin position in position in any suitable' manner, as by a nut 75. Thepiston 74 preferably is provided with a suitable sealing ring 76, suchas a conventional O-ring, and this assembly is slidably mounted withinan air cylinder 77. The cylinder 77 and the piston assembly on theextension yoke provide a means for quickly raising the extension yokeand returning it to its uppermost or zero position under certainoperating conditions. This quick return of the extension yoke isobtained by supplying air to the cylinder on the lower side of thepiston 74 adjacent to the driving portion of the extension yoke and iscontrolled by a suitable double-acting valve A Preferably, thequicloreturn mechanism is rigidly mounted on the filament puller housing33 through a mounting flange '78 at the lower end of the cylinder 77arranged in engagement with the upper surface of the collar 68. Thismounting flange also locks a sealing 0r stufiing box bushing 79 betweenthe flange 78 and the sides of a recess in the upper side of the collar68. This assembly is secured together in any suitable manner, as bystuds 80 which extend through the mounting flange 78, the collar 68, andthe housing cover 69. This forms a sealed air chamber within thecylinder 77 between the piston sealing ring 76 and the sealing bushing79.

Air pressure is adapted to be supplied into the cylinder 77 from anysuitable source for retraction drive of the extension yoke by the piston74 and to be vented from the cylinder 77 when the extension yoke isdriven downwardly by the drive motor M through a suitable tube 81, whichcommunicates with the interior of the cylinder 77 through a passageway81 in the mounting flange 78 and is sealingly secured thereto by aclamping nut 82. The double-acting valve A for control of the supply ofair pressure to the cylinder 77 and the venting of this cylinder mayconveniently be a solenoid type valve. Any suitable valve of this typemay be used and is schematically illustrated in FIG. 2 as comprising avalve body 83 within a valve housing 84 connected to the cylinder airpressure supply tube 81 and constructed so as to provide communicationbetween the cylinder 77 through the air supply tube 81 alternately withan air pressure supply 85 and a vent 86 to the atmosphere.

In this manner, when it is desired to operate the extension yoke 20 fora quick-return retraction thereof, air pressure is admitted into thecylinder 77 through the solenoid valve A from the air supply source 85by raising the solenoid valve body 83. This actuates the piston 74-toits uppermost position in the cylinder 77 and draws the extension yokeupwardly at a relatively rapid rate, thus causing an overriding of thecrown tooth mechanical portion of the extension yoke clutch GL The upperend 87 of the cylinder 77 is formed with a vent passage 88 to allow theexhaust of air from the cylinder 77 above the piston 74 during theretraction or upward stroke of the piston as it is actuated by airpressure on the lower side thereof. In order to cushion the piston 74 asit reaches the end of its upward stroke in the cylinder 77, the upperend of the extension yoke 20 is formed as a small plunger 89 of adiameter smaller than the threaded shoulder 73 and slightly smaller thanthe vent passage 88, so that as the piston 74 approaches the upper endof its stroke, the plunger 89 enters the vent passage 88 therebyrestricting the escape'of air out of the cylinder 77 above the piston74-. This causes a slight compression of the air entrapped in thecylinder 77 above the piston 74 and has a dashpot cushioning effect onthe final portion of the return travel of the piston and thereforeslowly retards the quick return of the exten sion yoke as it approachesits uppermost or zero position.

In a tensile tester for the measurement of stress-straincharacteristics, it is desirable to obtain an indication of both thestress placed on the test specimen and the resultant strain thereof. Inorder properly to evaluate these two factors, a record of thesimultaneous values thereof should be made so that their correlation canbe readily determined. It is important, therefore, that both the stresson the specimen and the resultant strain or elongation thereof bemeasured.

In the illustrated embodiment of the present invention, stress is placedon a specimen filament d by moving apart the two tabs 5 and 6 which aresecured to the ends of the filament. The stress on the filament ismeasured by the strain gage 12, which transmits an electrical signalproportional to this stress over conductors 27 to the recorder 3. Thestrain of the specimen filament 4 resulting from such stress can bemeasured in terms of the movement of the extension yoke 2% which placesthe stress on the filament. This movement of the extension yoke cannotbe measured directly as a displacement of the yoke from its initial orzero position, as in this ini-' tial position a test specimen 4 wouldnot be stressed, and it is only after the extension yoke has been drivendownwardly some distance that the extension yoke exerts a tension on thespecimen filament 4. It is therefore necessary to determine the positionof the extension yoke at which a measurement of the strain or elongationof a specimen is to begin. This is facilitated if the length ofspecimens to be tested is standardized; that is, if the length betweenthe points of attachment of a filament to the holding means, such as thetabs 5 and 6, is substantially fixed, so that the results of any set oftests for a given gage length can be readily compared. In this way it ispossible to measure the strain or elongation of a test specimen 4 inrelation to its original unstressed gage length. This can be done bymeasuring the movement of the extension yoke 20 after it begins to exerta stress on the specimen filament 4 or after it has exerted apredetermined percentage of stress on the test specimen.

In order thus to measure the elongation of a test specimen, theextension yoke 20 is connected to a measuring device through a clutchwhich provides for corresponding movement of the driving member of theclutch, while the driven member of this clutch is adapted to transmitpower to a driven shaft only after the extension yoke places stress onthe test specimen. Measurement of the movement of the driven member ofthe clutch, therefore, will provide a direct measurement of theelongation or strain on the test specimen filament 4 after it has beenstressed.

This strain measuring device drive mechanism includes a spur gear 90drivingly mounted on the main drive shaft 63 which drives the gear rackof the extension yoke 20 through the gear 65. Motion of the spur gear 90is transmitted to a clutch drive gear 91 through an idler gear 92mounted on a stub shaft 93. The clutch drive gear 91 is drivinglymounted on a clutch drive shaft 94 of a suitable type ofclutch CL whichpreferably is of the electromagnetic type, as this provides for a simplecontrol which can be readily correlated with the remainder of thetensile tester.

Such an electromagnetic clutch comprises a driven member 95 mechanicallyconnected to the main drive shaft 63 through the gear train includingthe gears 90,

' provided for energizing the electromagnetic clutch GL for transmittingpower from the driven member to an elongation measuring device through acooperating electromagnetic clutch member 96 and a clutch driven shaft97. The elongation measuring device may conveniently comprise apotentiometer and, in the illustrated embodiment, includes a three-turnpotentiometer 98 which is energized by any suitable source of electricalpower, such as a battery 99. The elongation measuring potentiometer 98is adapted to be driven from the clutch driven shaft 97 through suitablegearing, which is pref erably mounted on the exterior of the filamentpuller housing 33, so as to provide for easy replacement andinterchangeability. In this manner, gear trains having different gearratios may be quickly and easily substituted for driving thepotentiometer from the clutch driven shaft 97 in accordance with theexpected or possible strain of specimens being tested. Thus, ifrelatively little elongation or strain may be expected of a testspecimen, the elongation between zero stress and the ultimate strengthof the specimen can be magnified for bet ter analysis by a proper choiceof gearing between the driven shaft 97 of the clutch CL and theelongation measuring potentiometer 98. This gearing normally willinclude a spur gear 100 drivingly mounted on the driven shaft 97 of theclutch GL and an idler gear 101, rotatably mounted on a stub shaft 102secured to the filament puller housing 33 in any suitable manner, as bya screw 103, for transmitting motion from the spur gear 160 to apotentiometer drive gear 104, which is drivingly mounted on apotentiometer shaft 1%. The potentiometer shaft 1% is rotatablysupported in any suitable manner, as by bearings 106 and 197 mounted inthe filament puller housing 33.

In this manner, whenever the exciting winding of the elongationpotentiometer clutch GL is energized as a result of stress being placedon 'a test specimen, further movement of the extension yoke 20 willresult in a proportional movement of the elongation potentiometer so asto provide an electrical signal to conductors 198 and 109 fortransmittal to the recorder 3 for providing an indication of the strainon the test specimen 4. This may be conveniently obtained by mounting apotentiometercontactor 110 on the elongation potentiometer shaft 105, sothat the potential across the conductors 168 and 169 is directlyproportional to the position of the potentiometer contactor 110 andtherefore is directly proportional to the strain on the test specimenfilament 4.

In the illustrated embodiment, the conductors 108 and 109 areconveniently connected to an X-axis drive control 111, which directlycontrols the operation of a servo-motor 112 mechanically connectedthrough a suitable drive mechanism to a recorder pen 113. This pen drivemechanism may conveniently comprise a motor drive shaft 114 adapted todrive a drum 115 which transmits a proportional motion to the recorderpen 113 through a suitable driving cable 116, which extends around thedrum 115 and a pair of idler pulleys 117 and 118. The driving cable 116may be secured to the recorder pen 113 in any suitable manner, as bybeing attached by a set screw to finger 119 on the pen.

A correlated control and energizing electrical system is provided whichfacilitates arranging the three major components comprising the tensiletester for performing a variety of tests and for indicating or recordingthe test results on different indicating or recording instruments, asmay be required by the nature of the tests being performed. To this enda single source of alternating current power supply preferably isconnected to the electrical system of the tensile tester through asingle plug type terminal 12-9, which can readily be inserted into anysuitable outlet for connection to power supply lines L and L In thismanner the power supply is trans- 13 mitted through a suitable flexibleconductor 121 to the remote control box 2, and a main switch S isadapted to open and close the circuit of the tensile tester to thesource of supply through the conductor 121.

The control circuits from the remote control box 2 which govern theenergization of the filament puller opcrating devices are readilyconnectable to the filament puller system through a flexible cable 122and a plug type terminal 123 containing the proper number of conductorsand connectors for completing the desired circuits. Signals from thefilament puller 1 are adapted to be transmitted to the recorder 3through a suitable flexible cable 124, which also is is provided with aplug type terminal 125 for easy connection with a corresponding socketin the recorder. Where a recorder 3 is provided with various types ofautomatic controls which are responsive to certain conditions indicatedby the recorder, suitable electrical signals are adapted to betransmitted from the recorder 3 to the remote control box 2 through asuitable flexible cable 126, which is connected to the recorder througha plug type terminal 127. Where desired, both ends of the cables 122,124, and 126 may be provided with plug type terminals, although in mostinstances it will be sufiicient if only one end of these cables isprovided with a plug type terminal While the other end of the cable ispermanently connected to the electrical circuits of the filament puller1, the remote control box 2, or the recorder 3.

I When it is desired to operate the tensile tester, the main switch S isclosed and the motor switch S also is closed, thereby connecting oneterminal 128 of the motor M to the line L The drive motor M preferablyis of the reversible synchronous type and is provided with terminals 129and 129 which are alternately adapted to be energized in addition to theterminal 128 to provide for opposite directions of rotation of the drivemotor. These terminals 129 and 129' of the motor are adapted to beconnected to the other side L of the power supply through a motordirection relay Ry A condenser C is connected across the motor windingterminals 129 and 129 so as to produce the desired phase shift forriving the motor in the desired manner.

The exciting windings of both the extension yoke clutch GL and theelongation measuring potentiometer clutch GL are direct current windingsand therefore are adapted to be connected to the alternating currentsource of supply through a suitable rectifier circuit. A terminal 131 ofthe clutch GL and a terminal 132 of the clutch GL are adapted to beconnected to the line L of the source of electrical power through themain switch S and a second terminal 133 of the clutch GL and 134 of theclutch CL are adapted to be connected respectively through a masterrelay Ry and an elongation potentiometer clutch relay Ry to therectifier circuit. The illusrated rectifier circuit includes a resistorRS and a rectifier D adapted to be connected to line L of the source ofelectric power supply through the main switch S Condensers C and C areconnected to opposite ends of the resistor RS and are adapted to beconnected to line L of the source of electrical power supply through themain switch S In this manner all of the electrical energization of thedriving parts of the filament puller can be supplied from a singlesource of alternating current electrical power supply through the mainswitch S A tensile tester made in accordance with the present .invfi'tion is particularly adaptable for testing specimens under variousenvironmental conditions. The flexible cables 122 and 124 which providethe electrical connections between the filament puller 1 andrespectively the remote control box 2 and the recorder 3 facilitate thearrangement of the filament puller within an environ- ..mental controlcabinet wherein the temperature and fluid surrounding the test specimencan be accurately controlled. Furthermore, the parts of the filamentpuller 14 which hold the ends of a test specimen and which are adaptedto be moved relative to each other for varying the tension in thespecimen preferably are made of suitable non-corrosive material, such asstainless steel, so that tensile tests of specimens can be conductedwith the specimen completely immersed in any desired liquid, such aswater 135, in a suitable receptacle 136.

In order to facilitate the placement of a test specimen in a container,such as the water receptacle 136, the filament puller housing 33is'adjustably mounted on a supporting post 137 preferably rigidlysecured to a suitable base 138. The filament puller housing 33 isadjustably mounted on the post 137 by a pair of suitable brackets 139,which provide for ready adjustment of the vertical position of thefilament puller to facilitate placing a test specimen 4 in anenvironmental container.

In order to perform a complete tensile test of a speci men filament, thefirst step is to determine the den'ier of the filament in any suitablemanner. The denier potentiometer R then is set by adjusting thepotentiometer dial 29 to the denier of the sample filament, and thefilament is mounted on the filament puller 1 between the strain gagetension bar hook 9 and the extension yoke claws 16. The filament puller1 or the specimen-holding parts thereof are then placed in the desiredenvironment for conducting the test, after which the main power switch Sand the motor switch S are closed. A motor pilot light LM on the remotecontrol box is lit when the motor power switch S is closed, thusindicating that the motor is in condition for driving the extension yokeof the filament puller to start a tensile test of the specimen.

The test may be begun by depressing the button of a starting switch SThis switch comprises a contactor 140 which is adapted to close anenergizing circuit from the power line L through a set of contacts 141so as to energize an exciting winding 142 of the double-acting solenoidair valve A which controls the air supply to the extension yokequick-return cylinder 77. The other side of the solenoid valve excitingwinding 142 is connected directly to the other line L through the mainswitch S This causes the solenoid valve A to move to its upper positionas shown in FIG. 2, thereby closing the vent 86 of the air cylinder 77and connecting this cylinder to the air pressure supply 85. This assuresthat the extension yoke 20 is fully returned to its initial or zerostarting position and places a reverse torque on the driven member ofthe crown tooth portion of the extension yoke clutch GL through the gear65 and the main drive shaft 63. This is desirable as it assures apositive mechanical engagement of the mechanical drive through the crowntooth portion of the extension yoke clutch and avoids the possibility ofslippage therethrough. I

The starting switch S also comprises a second contactor 143 which closesa circuit through contacts which connect the power line L to an excitingwinding 144 of the master relay Ry so as to energize this winding andactuate this relay. Energization of the master relay closes a series ofcircuits through three contactors 145, 146,

and 147. The contactor 146 closes the circuit between the terminal 133of the extension yoke clutch CL and the rectifier, thereby energizingthe exciting winding of this clutch which tends to drive the extensionyoke 20 downwardly through the main drive shaft 63, the gear 65, and thegear rack 66. This driving force on the extension yoke 20 is resisted bythe air pressure in the cylinder 77 on the piston 74 at the upper end ofthe extension yoke 20 and further assures a positive mechanical drivingconnection through the crown tooth portion of the clutch GL This actionusually will be only momentary in nature as pressure on the button ofthe starting switch S normally is of short duration, just sufiicient toobtain energization of the master relay exciting winding 144 and of thedouble-acting solenoid air valve coil 142.

Release of the starting switch button opens the circuits through thestarting switch contactors 140 and 143. This deenergizes thedouble-acting solenoid air valve coil 142 through the contactor 14) andreleases the magnetic actuation of the solenoid air valve which is thenmechanically returned by any suitable means, as by a spring, to theposition shown in FIG. 2, wherein the quick-return air cylinder 77 isvented through the solenoid air valve and the vent 86. 7

As soon as the master relay Ry exciting Winding 144 is energized afterthe starting switch S has been closed, the master relay contactor 147closes a holding circuit which is adapted to maintain energization ofits exciting winding 144- after'the starting switch S has been released.This holdingcircuit includes a series of circuit opening and closingswitches which are responsive to various conditions for controlling theoperation of the master relay and are normally in closed position at thetime that the master relay winding 14-4 is initially energized by thestarting switch. In this manner the exciting winding of the extensionyoke clutch GL is energized through the rectifier D and the master relaycontactor 146, so that the extension yoke is driven by the drive motor Min a direction which will tend to exert tension on a specimen filament 4mounted between the strain gage 12 and the extension yoke base holdingmember 14.

As soon as the extension yoke 20 has begun its downward travel, an upperlimit microswitch S7 is actuated to its closed circuit position so as toenergize a circuit extending through this upper limit switch to masterrelay contacts 148 which are closed through the master contactor 145.This circuit extends to the recorder and is connected to a microswitch Swhich normally is opencircuited at the initial stages of operation ofthe extension yoke 20.

Further downward movement of the extension yoke 20 under actuation ofthe drive motor M causes the specimen-holding base member 14 to take upany slack in the test specimen 4 and eventually to place stress thereon.When the specimen 4 is stressed, the tension therein is transmitted as aforce through the tension bar 11 to the strain gage 12, so that anelectrical signal is transmitted from the strain gage over conductors 27to the Y -axis drive control 28 of the recorder. This operates theconventional servo-motor recorder controls to provide energization of aservo-motor 149 through suitable conductors 150 connected to the remotecontrol box 2 and through this box to the source of electrical powersupply L -L This causes the servo-motor 149 to drive a recorder roll 151through suitable mechanical connections thereto to provde for movementof two-coordinate paper relative to the Y-axis of the paper. Theservo-motor 149 could be used to drive any suitable two-coordinate paperholder in the Y-axis of the paper and, in some instances, such a holdermight comprise a hat table. For illustrative purposes, the presentinvention is shown in connection with a roll type paper holder of aconventional X-Y recorder 3, similar to that illustrated and describedin Patents 2,464,708 and 2,835,858-Moseley. Such recording instrumentsalso are illustrated and described in a publication by the L. F. MoseleyCompany in a manual entitled Autograf XY Recorder.

All such recorders are provided with certain basic features, such as thepen 113 of any suitable type for drawing a curve on coordinate draftpaper mounted on the paper holder of the recorder. The pen 113 isadapted to move relative to the coordinate paper in two differentdirections, generally indicated as the X and Y coordinate axes of thepaper. In certain types of recorders, the paper may be held stationaryand the pen moved relative thereto in both directions. In other types ofXY recorders, such as that illustrated, the coordinate paper is drivenin one direction by a se1vo-motor, such as the servo-motor 149, and thepen 113 is driven along the other axis by another servo-motor, such asthe servo-motor 112. In this .the remote control box and manner, a curvedrawn on coordinate paper by the pen 113 in response to the relativemovement between the paper holder and the pen gives a definiterelationship to the X and Y axes of the paper which bears a directrelationship to the signals received from external sources by the X andY axis drive controls. The Y axis relationship in the illustrated systemis provided by the electrical signal received by the recorder from thestrain gage 12 over the conductors 27, and the X-axis relationship isprovided by electrical signals supplied to the recorder from theelongation measuring potentiometer 93 over conductors 198 and M29.

Since the movement of the yoke 2t? from its initial or zero position tothe position of the base 14 when it initially places stress on aspecimen filament 14 may vary slightly with different specimens, andsince different specimens may have slightly erratic initial straincharacteristics at relatively low stress resulting from various causes,such as crimp or other slight non-uniform physical configurations ofspecimens, it is desirable that the stress-strain curves recorded on thecoordinate paper should, where possible, eliminate such initial erraticportions and thereby provide stress-strain curves which can be morereadily compared. This can conveniently be done by using circuitry whichwill prevent recordation of stress-strain results until the stress on atest specimen reaches a predetermined minimum value. It has been foundthat for most single fibers the erratic portions of stress-strain curveoccur below 2 percent stress on the specimens. Thus, by eliminating therecordation of strain of test specimens below 2 percent stress, thedesired stress-strain curves can be recorded by the recorder pen 113,and the curves then may be extrapolated to indicate the normalstress-strain relationships which would occur below this 2 percentstress.

A very simple manner of obtaining a cut-ofi of the strain during theinitial 2 percent stress on a test specimen is to mount a microswitch Sin the circuit which is responsive to the stress on the test specimen,and arranging this'microswitch S so that it will remain open belowpercent stress on the test specimen and will close a circuit above thispredetermined minimum stress, so as to 1nit1ate recordation of thestrain. In a system such as that illustrated in the drawings, whereinthe stress is plotted on the stress-strain coordinate paper along the Y-axis, the microswitch S can conveniently be placed on the recorder in aposition so that it can be actuated by the operation of the recorder toa 2 percent stress position. In the conventional recorder provided witha roll 15l on which the coordinate paper is mounted and in which theangular position of the roll 151 indicates the Y coordinate or stress,it has been found very convenient simply to mount the microswitch Sadjacent to an end of the roll 151 and operable by it. This can readilybe done by arranging an operating finger 152 of the microswitch in aposition engageable by an element of the roll 151 such that when theroll 15]; has moved from its zero position through an anglecorresponding to 2 percent stress, the microswitch S will close anelectrical circuitwhich will initiate the indication and recordation ofstra n ot the test specimen, This strain indicating initiatlngcircuit iseasily traced by reference to FIG. 2 as extending from the source ofelectrical power L through the switch S to the upper rack limitmicroswitch S through this switch to the master relay contacts 148 andits contactor 145, through the recorder 2 percent strain microswitch Sto an excitlng winding 153 of an elongation potentiometer clutch relayRy to power line L This energizes relay Ry and closes a circuit throughits contactor 154 which energizes the exciting winding of the elongationpotentiometer clutch GL through the rectifier D thereby providing formechanically driving the elongation potentiometer contactor 110. Thisenergization is indicated to the test operator by energization of apilot light LM on the remote control box 2, which is connected inparallel with the relay winding 153. In this manner, the potentiometercontactor 110 will be moved proportional to the rotation of the maindrive shaft 63 and therefore proportional to the actuation of theextension yoke gear rack 66 when the clutch GL is energized, thusproviding a direct relationship between the voltage across thepotentiometer 98 and the strain on the test specimen 4 for strain of thetest specimen over 2 percent stress thereon. Thus, the recorder pen 113of the illustrated recorder 3 will be moved along a supporting guide bar155 by the servomotor 112 in direct proportion to the strain on a testspecimen above 2 percent stress, and strain will be indicated by thecurve recorded by the pen on the coordinate paper mounted on therecorder roll 151.

In order to protect the tensile tester against accidental damage due tovarious factors which might cause certain parts of the tensile tester tobe operated beyond predetermined maximum safe limits of operation, aseries of operational limit switches are included in the controlcircuitry. These limit switches may be generally arranged in a seriescircuit which is adapted to deenergize the holding circuit of the masterrelay R372 when any of the limiting conditions is reached. Thisoperational limiting holding circuit preferably comprises switches whichare operable for deenergization of the master relay Ry to provide forinitiation of the quick-return operation of the extension yoke 20 inresponse to full extension of the extension yoke, to full 100 percentoperation of the elongatin measuring potentiometer 98, to a decrease intension of the test specimen 4 as indicated by the tension indicatingoperation of the recorder roll 151, such as when a stress reversaloccurs due to the breaking of a test specimen, to full scale operationof the stress indicating recording pen 113 by its movement to the end ofthe pen guide bar 155, and to a normally closed manually operablecontrol.

Specifically, this safety operational limit circuit may convenientlyinclude a normally closed microswitch S which is arranged to be operableby the extension yoke to open this circuit when the extension yoke hasmoved to its maximum lower 100 percent rack limit position. This lowerrack limit microswitch S may be of any suitable type and may include anoperating finger 156 which is engageable by a part of the extension yoketo open this normally closed microswitch at the lower limit of theextension yoke rack movement. The operational limit circuit can extendfrom the lower rack limit microswitch S to a normally closed microswitchS which is adapted to be opened in response to full 100 percentoperation of the elongation measuring potentiometer 110. This 100percent potentiometer position limiting switch normally is held inclosed circuit position and may conveniently be operated to open-circuitposition by a cam 157 drivingly mounted on the potentiometer shaft 105and arranged in engagement with a switch operating finger 157'. Theoperational limit circuit may then extend from the microswitch S in thefilament puller to a microswitch S on the recorder, which is adapted tobe maintained in closed circuit position during forward drive of therecorder roll 115. This position of the microswitch S may convenientlybe made responsive to the direction of drive of the roll 115 byarranging an operating finger 158 of the microswitch S in engagementwith a friction operating surface 159 on the roll 151, so that forwarddrive of the roll 151 biases the switch S to closed circuit position.This switch S readily serves to stop the normal operation of the tensiletest when a stress reversal is indicated on the recorder 3 by a reverserotation of the roll 151. Since a stress reversal will be indicated whena conventional tensile test is completed on the rupture of a testspecimen 4, the recorder roll will tend to be rotated in a reversedirection and the friction surface 159 will bias the microswitch finger158 so as to open the microswitch S The operational limit circuit alsocan be used to protect the recorder against an attempt to continue atensile test beyond the recording limits of the instrument by arranginga normally closed microswitch S connected in series with the stressreversal microswitch S This microswitch S is readily operable toopen-circuit position by arranging an operating finger 160 thereof forengagement by a portion of the recording pen 113 when the operating penreaches its full scale deflection at the end of its guide bar 155.

In order to assure against possible damage to the tensile tester due tounforeseen circumstances, the operation- 211 limit holding circuit forthe master relay Ry preferably also includes a normally closed manuallyoperable switch S connected in series with the various operationallimiting microswitches. This manually operable safety switch Spreferably is arranged in the remote control box 2 in a position nearestto the operator of the tensile tester, and in series with the masterrelay holding circuit contacts which are adapted to be closed by thecontactor 147.

In this manner, whenever one of the four specified limiting conditionsoccurs or the manually operable switch S is opened, the holding circuitof the master relay Ry will be opened so as to deenergize the masterrelay exciting winding 144. Deenergization of the exciting winding 144causes the master relay contactor-s 147 and 146 respectively to open theholding circuit of the relay exciting winding 144 and the energizingcircuit of the extension yoke clutch CL and to open the circuit betweenthe master relay contacts 148 through the contactor 145. Opening ofthese circuits respectively provides for mechanically disconnecting thedrive between the drive mo tor M and the extension yoke 20 through theextension yoke clutch GL which stops further extension of the filamentpuller; opening of the holding circuit through the master relaycontactor 147, which prevents reenergization of the extension yokeclutch 0L except under direct manual control by a manually operableswitch, such as the manually operable starting switch S or some othermanually operable switch for controlling the perfomance of hysteresistests.

Opening of the circuit through the master relay contacts 148 by itscontactor 145 removes the control of energization of the elongationpotentiometer relay exciting winding 153 from the master relay, so thatthis relay Ry would be opened if its exciting winding 153 were notprovided with a holding circuit. Such a holding circuit for theelongation potentiometer clutch relay is desirable, as the elongationpotentiometer contactor should be returned to its Zero position after atensile test has been completed, so that it will be ready for theindication of the strain on a test specimen when another test is begun.Such a holding circuit for the exciting winding 153 of the relay Ry isprovided through a normally closed manually operable switch S acontactor 161 of the relay Ry and an elongation potentiometer zeroposition limit microswitch S This holding circuit is closed when therelay exciting winding 153 is energized and the elongation measuringpotentiometer contactor 110 moves away from its zero position.

In order to obtain the safety control feature of this holding circuit,the potentiometer zero position microswitch S may conveniently beprovided with an operating finger 162 arranged in engagement with anoperating cam 163 drivingly mounted on the potentiometer shaft 105,which is constructed and arranged to open the microswitch S when theelongation potentiometer is in its zero position and to close it for allother positions of the potentiometer.

Whenever the master relay exciting winding 144 is deenergized inresponse to any of the operational limiting conditions or by themanually operable switch S the master relay contactor closes the circuitthrough contacts 164. This normally will occur at a time when theextension yoke 20 is moved downwardly from its zero extension position,so that the microswitch S is in its closed circuit position, therebyproviding an energizing circuit through the switch S the contactor 145,and contacts 164 for the two-way solenoid air valve energizing winding142. This actuates the air valve 83 to its upper position as viewed inFIG. 2, so as to close communication between the vent 66 and thequick-return cylinder 77 and provide air pressure into the cylinder 77through the valve 83 from the air supply 85. This serves 'to provide fora quick retraction of the extension yoke 2t? by the quick-return piston74, as has been previously explained. Retraction of the extension yokein this manner causes the reverse rotation of the drive gear 65 by theupward movement of the extension yoke gear rack 66, and thus causes themain drive shaft 63 to rotate in the reverse direction from its normalforward operation. This reverse rotation of the main drive shaft 63 istransmitted through the elongation potentiometer clutch GL to thepotentiometer shaft 1%, so as to return the potentiometer contactor 11%to its zero or initial starting position.

In most instances it will be found that the elongation potentiometercontactor 110 will be returned to its initial or zero position, shown inFIG. 2, before the extension yoke 20 reaches its initial or zeroposition, also shown in this figure, for the reason that thepotentiometer contactor 110 will not have been driven from its zeroposition until after the extension yoke 20 has traveled downwardly so asto apply a predetermined stress, such as 2 percent stress, on a testspecimen. It, therefore, will be returned to its zero positioncorrespondingly sooner than will the extension yoke 20. In order toprevent damage to the elongation measuring potentiometer, it thereforebecomes necessary to stop the drive of the potentiometer contactor 114)prior to the complete return of the extension yoke 20 to its zeroposition. This can readily be accomplished through the zero positionlimit microswitch S which, as has been explained, is actuated to itsclosed position by the cam 163 mounted on the potentiometer shaft 105for all positions of the elongation potentiometer contactor 110 exceptwhen this contactor 110 is in its zero position. In this zero positionof the contactor 110, the cam 163 actuates the microswitch S through itsfinger 162 to open-circuit position, which deenergizes the holdingcircuit for the elongation potentiometer clutch relay exciting winding153, causing this relay Ry to open. This opens the energizing circuit ofthe exciting winding for the elongation potentiometer clutch CL anddeclutches the drive between the elongation potentiometer contactor 110and the main drive shaft 63. This immediately stops the rotation of theelongation potentiometer contactor 110 in its zero position and allowsthe free travel of the extension yoke to continue to its initial or zeroposition under the operation of the quick-return piston 74. When theextension yoke 20 reaches its zero position, a suitable element on theextension yoke, which may comprise an operating finger 165, engages afinger 166 of the upper rack limit microswitch S and biases it toopen-circuit position, thereby opening the energizing circuit of thedouble-acting solenoid air valve exciting winding 142 to end theretracting of the extension yoke.

The actuation of the elongation measuring potentiometer may be broughtunder manual control at any time while the extension yoke is actuatedaway from its zero or upper rack limiting position through the normallyclosed elongation potentiometer clutch manual stop switch S simply bydepressing this switch, which opens the holding circuit of theelongation potentiometer clutch relay exciting winding 153 and causesthis relay Ry to open so as to open the energizing circuit of theelongation potentiometer clutch CL Drive of the elongation potentiometercontactor 110 may similarly be manually started by closing a circuit forenergizing the elongation potentiometer clutch relay winding 153 bydepressing an operating button of a normally open elongationpotentiometer clutch manual starting switch $16, so

2% as to close a circuit which energizes the exciting winding 153 of theelongation potentiometer clutch relay Ry This energization of theexciting winding 153 of the relay Ry closes the relay contactor 154across relay contacts which energize the exciting winding of theelongation potentiometer clutch CL so as to provide a driving connectionof the elongation potentiometer contact with the main drive shaft 63. Inthis manner, operation of the elongation measuring potentiometer may bebrought under manual control by the manual start and stop switches S andS respectively. 7

Under certain circumstances, it may be desirable to stop a tensile testat a predetermined point and to return the extension yoke to its zeroposition. This can be readily done by manually disconnecting the holdingcircuit of the master relay exciting Winding 144 by depressing the pushbutton of the manually operable switch S When this siwtch S isopen-circuited, it opens the holding circuit of the master relay Ry ashas been explained, to energize the double-acting solenoid air valvecoil 142 and provide for the quick-return retraction of the extensionyoke 20 in the normal manner.

In addition to the usual tensile test for determining the modulus ofelasticity, yield point, and ultimate strength of test specimens, it isdesirable at times to obtain tensile hysteresis characteristics of testspecimens. The present invention is particularly adaptable to providefor obtaining such tests either automatically or manuall and for varyingthe maximum stress applied to a specimen in performing such tests. Thisis readily obtained by controlling the energization and deenergizationof the motor direction relay Ry either automatically by the recorder Ror by suitable manual push button switches.

The motor direction relay is adapted to connect the drive motorterminals 129 and 129' alternately to the power line L through the motordirection relay contactor 130 to provide for opposite directions ofrotation. This relay contactor 130 is adapted to close a circuit throughrelay contacts 167 for energization of the drive motor M through itsterminal 129 when the motor direction relay exciting winding 168 isdeenergized, as shown in FIG. 2, to provide for motor operation in aforward direction; that is, in a direction which will advance or lowerthe extension yoke 20 under normal driving engagement of the variousgears and clutches. This is the normal position for the motor directionrelay for the performance of tensile tests and can be used for manuallyplacing stress on a test specimen 4 in the performance of a tensilehysteresis test.

In order to perform a tensile hysteresis test, the stress reversalmicroswitch S is shunted out of circuit by a switch S This rendersinoperative the quick return of the extension yoke 20 due to stressreversal as indicated by reverse drive of the recorder roll 151. Manualhysteresis tests are readily performed by initially placing stress on atest specimen simply by depressing the starting switch S as for thecommencement of a normal tensile test, and, when the desired maximumstress has been placed on the test specimen, as indicated by the pen 113on the recorder 3, a normally open manually operable switch S in theremote control box is operated to its closed position by depressing itsoperating button. This completes a circuit through contactor 159 andcontacts 170 of the switch S so as to energize the motor director relayexciting Winding 168. This actuates the motor direction relay Ry so asto close a reverse drive motor circuit through the motor direction relaycontactor 130 and contacts 171, while opening the motor circuit throughcontacts 167. This position of the motor direction relay Ry energizesthe drive motor M through its terminal 129' for operation of the drivemotor in reverse; that is, in a direction which will retract theextension yoke 20 upwardly through the drive gear 65 and the main driveshaft 63. Such retraction of the extension yoke 20 by the drive motor Min no way provides for quick return of the extension yoke 20 through itsair piston 74. It simply relieves the stress on a test specimen 4 at thesame slow rate as the stress was initially applied to the test specimen,thereby preventing any suddent changes in the stress on the specimen.When the stress on the test specimen 4 has been reduced to zero, thehysteresis test may be continued by again stressing the test specimensimply by releasing pressure on the normally open manual switch S so asto open the circuit through its contacts 170, thereby deenergizing themotor direction relay exciting winding 168 and returning this relay tothe position shown in FIG. 2. In this position, the relay contactor 130again closes the drive motor energizing circuit through the relaycontacts 167 and the motor terminal 129 for forward drive of the drivemotor and downward actuation of the extension yoke 20. In this manner, atest specimen 4 may be repetitively stressed and relieved of stress orrelieved of such portion of the stress as may be desired and restressedto a higher or lower value during repeated stressing thereof to obtainthe characteristics of the specimen by such hysteresis tests.

Hysteresis tests also may be useful for the determination of effectswhich can be produced in certain types of materials by stressing beyondthe elastic limits of the material from repeated stressing above theelastic limit. All materials which are stressed to a value exceeding theelastic limit receive a deformation, some of which remains as apermanent set or elongation of the material after the stress has beenremoved. In the case of nonductile materials, overstressing of this typeusually causes permanent injury, and a few repetitions of such loadingoften is sufficient to cause rupture of the stressed element.

In some instances, if the material is stressed beyond the yield point,and the stress then relieved substantially, a restressing will show thatthe yield point has been raised and the deformation above the yieldpoint is decreased. In most instances, stress-strain tests of this typeare computed in terms of the original cross sectional area of a testspecimen. In the illustrated apparatus, the recorder 3 will indicate thestress-strain relationship in terms of unit cross sectional area, butthis will not be strictly accurate above the yield point, as the signalreceived by the recorder is proportional to the unit cross sectionalarea on the basis only of the original cross section of a test specimenas set by the denier potentiometer R Actually the new yield point of amaterial, which has been given a permanent deformation by having beenstressed beyond a yield point and then having the stress reducedsubstantially and then restressed, would be higher than the value whichwill be indicated by the recorder, as it is not practical to determinethe cross sectional area of a test specimen during a hysteresis test orduring a test with repeated stressing beyond the yield point of thematerial. If accurate indication of the new yield point is to be given,the denier potentiometer dial 29 on the remote control box 2 should bereset after each stressing of the specimen beyond its yield point, asthe permanent deformation acquired by the specimen not only includes apermanent elongation or strain, but also includes a permanent reductionin the cross sectional area, so that the stress per unit area actuallyis higher than that indicated in terms of the original area of the testspecimen.

Hysteresis tests of the type which have already been described can alsobe obtained automatically by the use of certain limit switches in therecorder for automatically reversing the drive motor M at apredetermined stress. Below the elastic limit the stress is proportionalto the strain, so that the reversal of the drive motor at apredetermined strain, as indicated by the strain of a test specimenbelow the elastic limit, and the automatic restressing of the specimenwhen the strain thereof has been reduced to zero will provide thedesired automatic hysteresis test. This may conveniently be done byatranging a normally open microswitch S adjustably mounted withreference to the recorder pen 113 and provided with an operating fingerI72 engageable by a part of the pen 113, as by an operating button 173on the pen finger 119. The microswitch S may be slidably mounted on asupporting bar 174, parallel to the pen guide bar 155, so that theswitch S can be set for operation to its closed position by engagementthereof by the recorder pen button 173 at any predetermined strain of atest specimen as indicated by the position of the recorder pen 113. Themicroswitch S is connected in a circuit extending from the power supplyline L to a terminal of the exciting winding 168 of the motor directionrelay Ry so as to energize this exciting winding when the switch S isclosed. Energization of the winding 168 actuates the motor directionrelay Ry so as to open the circuit of the drive motor M from itsterminal 129 through the relay contactor 134) and contacts 167 andcloses an energizing circuit for the drive motor M through its terminal129, the contactor 130, and contacts 171, thereby reversing thedirection of rotation of the drive motor M This results in a gradualreversal of the stress on the test specimen, as the operation of thequick return of the extension yoke 20 by the air piston 74 is renderedinoperative by the shunting of the stress reversal microswitch S throughthe switch S for all hysteresis tests.

In this position of the motor direction relay Ry a holding circuit formaintaining energization of the relay exciting winding 168 is providedthrough a relay contactor 1'75, which closes the circuit through relaycontacts 176, a normally closed push button switch S and a normallyclosed zero strain microswitch S If it is desired to stop the stressreducing part of the test before the strain has been reduced to zero andautomatically to restress the specimen, this can easily be done bysimply depressing the push button of the manually operable switch S onthe remote control box 2, so as to deenergize the relay exciting winding168 through its holding circuit. This holding circuit normally will bebroken by the zero strain microswitch S in the recorder by engagement ofan operating finger 177 of the microswitch S by the pen 113 when it isreturned to its zero strain position.

In this manner the hysteresis characteristics of a specimen may beeasily determined automatically by presetting the adjustable microswitchS to the desired maximum strain on a specimen, with the stress reversalmicroswitch S shunted by closure of the switch S then automaticallystarting the test by closing the starting switch S Closure of startingswitch S causes the drive motor M to be operated in a forward directionin the usual manner, so as to provide for downward actuation of theextension yoke 20 for the application of stress on a test specimen 4mounted on the filament puller 1. The recorder 3 will record thestress-strain relationship of the test in the usual manner until therecorder pen 113 actuates normally open microswitch S to closedposition, so as to energize the exciting winding 168 of the motordirection relay Ry to provide for reverse drive of the drive motor M ashas been explained. The automatic repetition of the stressing andreduction of stress of the test specimen will continue between the zerostrain position and the predetermined maximum strain position as set bythe limit switch S until the test specimen 4 is fractured or until thetest is stopped by opening of switch S or S on the remote control box.

In this manner, automatic hysteresis tests, as well as manual hysteresistests, may be readily obtained by the illustrated embodiment of thepresent invention, in addition to direct stress-strain characteristictensile tests, and all such tests can be conducted with an apparatuswhich is adapted to perform these tests on specimens in ambients arseaes23 which may be controlled as to both temperature and humidity or otherfluid environments.

While a particular embodiment of this invention has been illustrated anddescribed, modifications thereof will occur to those skilled in the art.It is to be understood, therefore, that this invention is not to belimited to the particular details disclosed, and it is intended in theappended claims to cover all modifications Within the spirit and scopeof this invention.

What is claimed is:

1. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for tensioning a specimen held by saidholding means including a reversible drive; means for indicating tensionon a specimen; means for indicating elongation of a specimen; aquick-return retraction drive means for said tensioning meansindependent of said reversible drive; a normally-closed manual controlmeans of said quickreturn retraction drive means; and means forinitiating operation of said quick-return means in response to fullextension of said tensioning means, to decrease in tension on aspecimen, to full scale operation of said tension indicating means, andto opening of said nornially-closed manual control means.

2. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means including an extension yoke with areversible motor drive for tensioning a specimen held by said holdingmeans; means for indicating tension on a specimen; means for indicatingelongation of a specimen; a quick-return retraction drive means for saidextension yoke independent of said drive motor; a normally-closed manualcontrol means for said quick-return retraction drive means; and meansfor initiating operation of said extension yoke quick-return means inresponse to full extension of said extension yoke, to decrease intension as indicated by said tension indicating means, to full scaleoperationof said tension indicating means, and to opening of saidnormally-closed manual control means.

3. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for tensioning a specimen held by saidholding means, said tensioning means including an extension yoke with areversible drive motor, means for indicating tension on a specimen;means for indicating elongation of a specimen; and means for obtainingtension hysteresis characteristics of a specimen including automatic andmanual controls, said automatic controls comprising means responsive toa variable predetermined maximum tension indication by said tensionindicating means for energizing said motor for reverse drive and meansresponsive to zero tension indication for energizing said motor fortensioning for- Ward drive, said manual controls comprising manuallyoperable means for energizing said motor in opposite drive directions.

4. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means including an extension yoke With areversible motor drive for tensioning a specimen held by said holdingmeans; means for indicating tension on a specimen; means for indicatingelongation of a specimen; a quick-return re-.

traction drive means for said extension yoke independent of said drivemotor comprising an air cylinder having a piston therein connected tosaid extension yoke, means for supplying air pressure to said cylinderon one side of said piston for retraction drive thereof, a vent in saidcylinder on the side of said piston away from the air pressure sidethereof, means for controlling the supply of air pressure to saidcylinder and for venting said cylinder on the air-pressure side of saidpiston; a normally-closed manual;

control means for said quick-return retraction drive means;

and means for initiating operation of said extension yoke quick-returnmeans in response to full extension of said extension yoke, to decreasein tension as indicated by said tension indicating means, to full scaleoperation of said tension indicating means, and to opening of saidnormallyclosed manual control means.

5. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for tensioning a specimen held by saidholding means, said tensioning means including an extension yoke with areversible drive motor, means for indicating tension on a specimen;means for indicating elongation of a specimen; means for obtainingtension hysteresis characteristics of a specimen including automatic andmanual controls, said automatic controls comprising means responsive toa variable predetermined maximum tension indication by said tensionindicating means for energizing said motor for reverse drive and meansresponsive to zero tension indication for energizing said motor fortensioning forward drive; said manual controls comprising manuallyoperable means for energizing said motor in opposite drive directions; aquick-return retraction drive means for said extension yoke independentof said drive motor; a normally-closed manual control means for saidquick-return retraction drive means; means for initiating operation ofsaid extension yoke quick-return means in response to full extension ofsaid extension yoke, to decrease in tension as indicated by said tensionindicating means, to full scale operation of said tension indicatingmeans, and to opening of said normally-closed manual control means; andmeans for rendering inoperative said quick-return means response to saidindication of decrease in tension when said apparatus is under controlof said tension hysteresis characteristics means controls.

6. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen includingan extension yoke with a reversible drive means, a reversible drivemotor, means for providing a driving connection between said drive motorand said extension yoke; means for controlling said driving connectionincluding a master relay and a normallyopen manually-operable startingswitch for initially energizing said master relay on closure of contactsof said starting switch, means for measuring tension on a specimen;means (TIM) responsive to measurments of said tension measuring meansfor indicating said tension measurements; means for measuring elongationof a specimen; means (EIM) resopnsive to measurements of saidelongation-measuring means for indicating said elongation measurements;a quick-return retraction drive means for said extension yokeindependent of said drive motor; means providing a holding circuitincluding contacts of said master relay adapted to be closed onenergization of said master relay for normally maintaining energizationof said master relay after initial energization thereof by said startingswitch; a normally-closed manual control means in said holding circuit;said master relay holding circuit means comprising means operable fordeenergization of said master relay to provide for operation of saidextension yoke quick-return means in response to full extension of saidextension yoke, to full operation of said elongation-measuring means, todecrease in tension as indicated by said TIM, to full scale operation ofsaid TIM, and to opening of said normally-closed manual control means;said master relay having contacts adapted to close a circuit forenergizing said quick-return drive means on deenergization of saidmaster relay.

7. 'Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying in the specimen including anextension yoke with a reversible drive means, a reversible drive motor,means for providing a driving connection between said drive motor andsaid extension yoke; means for controlling said driving connectionincluding a master relay and a normally-open manually-operable startingswitch for initially energizing said master relay on closure of contactsof said starting switch, means for indicating tension on a specimen;means for indicating elongation of a specimen; a quick-return retractiondrive means for said extension yoke independent of said drive motor,said quick-return drive means comprising an air cylinder having a pistontherein connected to said extension yoke, means including a two-waysolenoid valve for controlling the supply of air pressure to saidcylinder and for venting said cylinder on the air-pressure side of saidpiston; means providing a holding circuit including contacts of saidmaster relay adapted to be closed on energization of said master relayfor normally maintaining energization of said master relay after initialenergization thereof by said starting switch; a normally-closed manualcontrol means in said holding circuit; said master relay holding circuitmeans comprising means operable for deenergization of said master relayto provide for operation of said extension yoke quick-return means inresponse to full extension of said extension yoke, to decrease intension as indicated by said tension indicating means, to full scaleoperation of said tension indicating means, and to opening of saidnormally-closed manual control means; and said master relay havingcontacts adapted to close a circuit for energizing said quick-returndrive means on deenergization of said master relay.

8. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen includingan extension yoke with a reversible drive means comprising a reversibledrive motor and means for providing a driving connection between saiddrive motor and said extension yoke; means for controlling said drivingconnection including a master relay and a normally-openmanually-operable starting switch for initially energizing said masterrelay on closure of contacts of said starting switch, means formeasuring tension on a specimen; means (TIM) responsive to measurementsof said tension measuring means for indicating said tensionmeasurements; means for measuring elongation of a specimen; meansresponsive to measurements of said elongation measuring means forindicating said elongation measurements; a quick-return retraction drivemeans for said extension yoke independent of said drive motor, saidquick-return drive means comprising an air cylinder having a pistontherein connected to said extension yoke, means including a two-waysolenoid valve for controlling the supply of air pressure to saidcylinder and for venting said cylinder on the air-pressure side of saidpiston; means providing a holding circuit including contacts of saidmaster relay adapted to be closed on energization of said master relayfor normally maintaining energization of said master relay after initialenergization thereof by said starting switch; a normally-closed manualcontrol means in said holding circuit; said master relay holding circuitmeans comprising means operable for deenergization of said master relayto provide for operation of said extension yoke quick-return means inresponse to full extension of said extension yoke, to full operation ofsaid elongation measuring means, to decrease in tension as indicated bysaid TIM, to full scale operation of said TIM, and to opening of saidnormally-closed manual control means; said master relay having contactsadapted to close a circuit for energizing said quick-return drive meanson deenergization of said master relay; and means for varying theresponse of said tension measuring means in accordance with the crosssection of the specimen be- 26 ing tested for obtaining an indication oftension on a specimen in terms of stress.

9. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for tensioning a specimen held by saidholding means including means for moving said holding means relative toeach other; said moving means including an extension yoke with areversible gear drive, a reversible drive motor, means including a maindrive electromagnetic clutch (MDC) having positive clutching means forproviding a driving connection between said drive motor and said geardrive; means for energizing said MDC including a master relay and anormally-open manually-operable starting switch for initially energizingsaid master relay, said master relay having contacts for closing anenergizing circuit for said MDC on energization of said master relay andbreaking said MDC energizing circuit on deenergization of said masterrelay; means for measuring tension on a specimen; means (TIM) responsiveto measurements of said tension measuring means for indicating saidtension measurements; means for measuring elongation of a specimen;means (EIM) responsive to measurements of said elongation measuringmeans for indicating said elongation measurements; a quick-returnretraction drive means for said extension yoke independent of said drivemotor comprising an air cylinder having a piston therein connected tosaid extension yoke, means for supplying air pressure to said cylinderon one side of said piston for retraction drive thereof, a vent in saidcylinder on the side of said piston away from the air-pressure sidethereof, means including a solenoid valve for controlling the supply ofair pressure to said cylinder and for venting said cylinder on theairpressure side of said piston; and said starting switch havingcontacts for initially energizing said solenoid valve to air-pressureadmitting position on closure of said switch prior to tensioningmovement of said extension yoke for exerting a force resisting anextension drive through said MDC to assure positive initial engagementthereof; means providing a holding circuit including contacts of saidmaster relay adapted to be closed on energization of said master relayfor normally maintaining energization of said master relay after initialenergization thereof by said starting switch; a normally-closed manualcontrol means in said holding circuit; said master relay holding circuitmeans comprising means operable for deenergization of said master relayto initiate operation of said extension yoke quick-return means inresponse to full extension of said extension yoke, to full operation of.said elongation measuring means, to decrease in tension as indicated bysaid TIM, to full scale operation of said TIM, and to opening of saidnormally-closed manual control means; and said master relay havingcontacts for energizing said quick-return drive means on deenergizationof said master relay.

10. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the speci men; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen; saidmoving means including an extension yoke with a reversible gear drive, areversible drive. motor, means including a main drive electromagneticclutch (MDC) for providing a driving connection between said drive motorand said gear drive; means for energizing said MDC including a matserrelay and a normally-open manually-operable starting switch forinitially energizing said master relay on closure of contacts of saidstarting switch, said master relay having contacts for closing anenergizing circuit for said MDC on energization of said master relay andbreaking said MDC energizing circuit on deenergization of said masterrelay; means (TIM) responsive to the tensile force on a specimen forindicating said force per unit cross-sectional area; means responsive toelongation of a specimen for indicating said elongation; and means forautomatically obtaining tension hysteresis characteristics of a specimenincluding means responsive to a variable predetermined maximum tensionas indicated by said TIM for energizing said motor for reverse drive andmeans responsive to zero tension indication by said TIM for energizingsaid motor for forward tensioning drive whereby said motor isautomatically alternately operated in opposite directions as determinedby said maximum tension and zero tension indications of said TIM.

11. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen; saidmoving means including an extension yoke with a reversible gear drive, areversible drive motor, means including a main drive electromagneticclutch (MDC) for providing a driving connection between said drive motorand said gear drive; means for energizing said MDC including a masterrelay and a normally-open manually-operable starting switch forinitially energizing said master relay on closure of contacts of saidstarting switch, said master relay having contacts for closing anenergizing circuit for said MDC on energization of said master relay andbreaking said MDC energizing circuit on deenergization of said masterrelay; means for measuring tension on a specimen; means (TIM) responsiveto measurements of said tension measuring means for indicating saidtension measurements; means for measuring elongation of a specimen;means responsive to measurements of said elongation measuring means forindicating said elongation measurements; a quick-return retraction drivemeans for said extension yoke independent of said drive motor; meansproviding a holding circuit including contacts of said master relayadapted to be closed on energization of said master relay for normallymaintaining energization of said master relay after initial energizationthereof by said starting switch; a normallyclosed manual control meansin said holding circuit; said master relay holding circuit meanscomprising means operable for deenergization of said master relay toprovide for operation of said extension yoke quick-return means inresponse to full extension of said extension yoke, to full operation ofsaid elongation measuring means, to decrease in tension as indicated bysaid TIM, to full scale operation of said TIM, and to opening of saidnormally-closed manual control means; and said master relay havingcontacts for energizing said quick-return drive means on deenergizationof said master relay.

12. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen; saidmoving means including an extension yoke with a reversible gear drive, areversible drive motor, means including a main drive electromagneticclutch (MDC) for providing a driving connection between said drive motorand said gear drive; means for energizing said MDC including a masterrelay and a normallyopen manually-operable starting switch for initiallyenergizing said master relay on closure of contacts of said startingswitch, said master relay having contacts for closing an energizingcircuit for said MDC on energization of said master relay and breakingsaid MDC energizing circuit on deenergization of said master relay;means for measuring tension .on a specimen; means (TIM) responsive tomeasurements of said tension measuring means for indicating said tensionmeasurements; means (EMP) for measuring elongation of a specimen; meansresponsive to measurements of said elongation measuring means forindicating said elongation measurements, means including anelectromagnetic clutch for providing a driving connection between saidextension yoke drive gear and said elongation-measuring means; meansincluding a relay having contacts for energizing saidelongation-measuring means clutch (EMC) when said EMC relay (EMCR) isenergized; an EMCR initial energizing circuit including means responsiveto a predetermined minimum tension on a specimen as indicated by saidTIM serially connected with a normally-closed switch adapted to beopened in the fully retracted position of said extension yoke andcontacts of said master relay adapted to beclosed and opened when saidmaster relay is respectively energized and deenergized, means providinga holding circuit for maintaining energization of said EMCR includingEMCR contacts adapted to be closed on energiaztion of said EMCR and anormallyclosed switch adapted to be opened in the zero position of saidelongation-measuring means for deenergizing said EMCR; means forautomatically obtaining tension hysteresis characteristics of a specimenincluding motor reversing switch means responsive to a variablepredetermined maximum tension as indicated by said TIM for energizingsaid motor for reverse drive and means responsive to zero tensionindication by said TIM for energizing said motor for tensioning forwarddrive whereby said motor is automatically alternately operated inopposite directions determined by said maximum tension and zero tensionindications of said'TIM; a quick-return retraction drive means for saidextension yoke independent of said drive motor connected to saidextension yoke, means providing a holding circuit including contacts ofsaid master relay adapted to be closed on energization of said masterrelay for normally maintaining energization of said master relay afterinitial energization thereof by said starting switch; a normally-closedmanual control means in said holding circuit; said master relay holdingcircuit means comprising means operable for deenergization of saidmaster relay to provide for operation of said extension yokequick-return means in response to full extension of said extension yoke,to full operation of said EMP, to decrease in tension as indicated bysaid TIM, to full scale operation of said TIM, and to opening of saidnormally-closed manual control means; means for rendering inoperativesaid quick-return means response to said indication of decrease intension when said appa' ratus is under control of said tensionhysteresis characteristics means controls; and said master relay havingcontacts for energizing said quick-return drive means on deenergizationof said master relay.

13. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen; saidmoving means including an extension yoke with a reversible gear drive, areversible drive motor, means including a main drive electromagneticclutch (MDC) for providing a driving connection between said drive motorand said gear drive; means for energizing said MDC including a masterrelay and a normally-open manually operable starting switch forinitially energizing said master relay on closure of contacts of saidstarting switch, said master relay having contacts for closing anenergizing circuit for said MDC on energization of said master relay andbreaking said MDC energizing circuit on deenergization of said masterrelay; means for measuring tension on a specimen; means (TIM) responsiveto measurements of said tension measuring means for indicating saidtension measurements; means for measuring elongation of a specimen;means responsive to measurements of said elongation-measuring means forindicating said elongation measurements; means including anelectromagnetic clutch for providing a driving connection between saidextension yoke drive gear and said elongation-measuring means; meansincluding a relay having contacts for energizing saidelongationmeasuring means clutch (EMC) when said EMC relay (EMCR) isenergized; an EMCR initial energizing circuit including means responsiveto a predetermined minimum tension on a specimen as indicated by saidTIM serially connected with a normally-closed switch adapted to beopened in the fully retracted position of said extension yoke andcontacts of said master relay adapted to be closed and opened when saidmaster relay is respectively energized and deenergized, means providinga holding circuit for maintaining energization of said EMCR includingEMCR contacts adapted to be closed on energization of said EMCR and anormally-closed switch adapted to be opened in the zero position of saidelongation measuring means for deenergizing said EMCR; means forautomatically obtaining tension hysteresis characteristics of a specimenincluding motor reversing switch means responsive to a variablepredeterminable maximum tension as indicated by said TIM for initiatingenergization of said MDR with an MDR energization holding circuitcomprising MDR contacts closed on energization of said MDR and anormally-closed manually-operable forward-drive switch means and asecond motor forwarddrive switch means responsive to zero tensionindication by said TIM for deenergizing said MDR whereby said drivemotor is adapted to be automatically alternately operated in oppositedirections as determined by said maximum tension and zero tensionindicated by said TIM; a quick-return retraction drive means for saidextension yoke independent of said drive motor comprising an aircylinder having a piston therein connected to sa d extension yoke, meansfor supplying air pressure to said cylinder on one side of said pistonfor retractlon drive thereof, a vent in said cylinder on the side ofsaid piston away from the air pressure side thereof, means forcontrolling the supply of air pressure to said cylinder and for ventingsaid cylinder on the air-pressure side of said piston; means providing aholding circuit including contacts of said master relay adapted to beclosed on energization of said master relay for normally maintainingenergization of said master relay after initial energization thereof bysaid starting switch; a normally-closed manual control means in saidholding circuit; said master relay holding circuit means comprisingmeans operable for deenergization of said master relay to initiateoperation of said extension yoke quick-return means in response to fullextension of said extension yoke, to full operation of saidelongation-measuring means, to decrease in tension as indicated by saidTIM, to full scale operation of said TIM, and to opening of saidnormallyclosed manual control means; means for rendering inoperativesaid quick-return means response to said indication of decrease intension when said apparatus is under control of said tension hysteresischaracteristics means controls; said master relay having contacts forenergizing said quick-return drive means on deenergiaztion of saidmaster relay; and means for varying the response of said tensionmeasuring means in accordance with the cross section of the specimenbeing tested for obtaining an indication of tension on a specimen interms of stress.

14. Apparatus for testing the tensile properties of specimens comprisingmeans for holding one end of a specimen; other means for holding theother end of the specimen; means for moving said specimen holding meansrelative to each other for varying the tension in the specimen; saidmoving means including an extension yoke with a reversible gear drive, areversible drive motor, means for energizing said drive motor includinga manually operable switch and a motor direction relay control means(MDR), said MDR having contact means for connecting said motor forforward drive when said MDR is deenergized and contact means forconnecting said motor for reverse drive when said MDR is energized,means including a main drive electromagnetic clutch (MDC) for providinga driving connection between said drive motor and said gear drive; meansfor energizing said MDC including a master relay and a normally-openmanually-operable starting switch for initially energizing said masterrelay by closure of contacts of said starting switch, said master relayhaving contacts for closing an energizing circuit for said MDC onenergization of said master relay and breaking said MDC energizingcircuit on deenergization of said master relay; means for measuringtension on a specimen; means for varying measurement response of saidtension measuring means in accordance with the cross section of aspecimen being tested for obtaining a measurement of tension in terms ofstress; means (TIM) responsive to measurements of said tension measuringmeans for indicating said tension measurements; means including apotentiometer for measuring elongation of a specimen; means responsiveto measurements of said elongation-measuring means for indicating saidelongation measurements; means including an electromagnetic clutch forproviding a driving connection between said extension yoke drive gearand said elongation-measuring potentiometer (EMP); means including arelay having contacts for energizing said elongation-measuringpotentiometer clutch (EMPC) when said EMPC relay (EMPCR) is energized;an EMPCR initial energizing circuit including means responsive to apredetermined minimum tension on a specimen as indicated by said TIMserially connected with a normally-closed switch adapted to be opened inthe fully retracted position of said ex tension yoke and contacts ofsaid master relay adapted to be closed and opened when said master relayis respectively energized and deenergized; means providing a holdingcircuit for maintaining energization of said EMPCR including EMPCRcontacts adapted to be closed on energization of said EMPCR and anormally-closed cam-operated EMP zero-position switch adapted to beopened in the zero position of said EMP for deenergizing said EMPCR; anormally-closed manually-operable switch for opening said EMPCR holdingcircuit; means including a normally-open manually-operable switch forindependently energizing said EMPCR; means for automatically obtainingtension hysteresis characteristics of a specimen including motorreversing switch means responsive to a variable predeterminable maximumtension as indicated by said TIM for initiating energization of said MDRwith an MDR energization holding circuit comprising MDR contacts closedon energization of said MDR and a normally-closed manually-operableforward-drive switch means and a second motor forward-drive switch meansresponsive to zero tension indication by said TIM for deenergizing saidMDR whereby said drive motor is adapted to be automatically alternatelyoperated in opposite directions as determined by said maximum tensionand zero tension indicated by said TIM; a normally-openmanually-operable switch means for energizing said MDR for obtainingreverse motor drive; a quick-return retraction drive means for saidextension yoke independent of said drive motor, said quick-return drivemeans comprising an air cylinder having a piston therein connected tosaid extension yoke, means for supplying air pressure to said cylinderon one side of said piston for retraction drive thereof, a vent in saidcylinder on the side of said piston away from the air-pressure sidethereof, means on said piston for reducing the venting action of saidvent as said piston approaches the end of its air-pressure actuatedretraction stroke for trapping a small amount of air as a cushionbetween said piston and the end of said cylinder, means including atwo-way solenoid valve for controlling the supply of air pressure tosaid cylinder and for venting said cylinder on the air-pressure side ofsaid piston; said starting switch having contacts for closing a circuitfor initially energizing said solenoid valve to air-pressure admittingposition on closure of said starting switch; means providing a holdingcircuit including contacts of said master relay adapted to be closed onenergization of said master relay for normally maintaining energizationof said master relay after initial energization thereof by said startingswitch; a normally-closed

1. APPARATUS FOR TESTING THE TENSILE PROPERTIES OF SPECIMENS COMPRISINGMEANS FOR HOLDING ONE END OF A SPECIMEN; OTHER MEANS FOR HOLDING THEOTHER END OF THE SPECIMEN; MEANS FOR TENSIONING A SPECIMEN HELD BY SAIDHOLDING MEANS INCLUDING A REVERSIBLE DRIVE; MEANS FOR INDICATING TENSIONON A SPECIMEN; MEANS FOR INDICATING ELONGATION OF A SPECIMEN; AQUICK-RETURN RETRACTION DRIVE MEANS FOR SAID TENSIONING MEANSINDEPENDENT OF SAID REVERSIBLE DRIVE; A NORMALLY-CLOSED MANUAL CONTROLMEANS OF SAID QUICKRETURN RETRACTION DRIVE MEANS; AND MEANS FORINITIATING OPERATION OF SAID QUICK-RETURN MEANS IN RESPONSE TO FULLEXTENSION OF SAID TENSIONING MEANS, TO DECREASE IN TENSION ON ASPECIMEN, TO FULL SCALE OPERATION OF SAID TENSION INDICATING MEANS, ANDTO OPENING OF SAID NORMALLY-CLOSED MANUAL CONTROL MEANS.